1. Field of the Invention
The present invention relates to a remote control system for the transmission of data, and more specifically for distant control of telegraphic reception equipment.
2. Description of the Prior Art
There are at present two commonly used methods of turning on a teletypewriter from a remote location. These two methods are: the use of a data modem on a switched telephone circuit; and the use of a private direct current loop line with a relay operated from rectified 30 cycle ringing super-imposed onto the direct current loop. The use of a data modem provides the required control but involves the use of complicated and sensitive equipment at both ends of the line. The second method is relatively simple and has found wide usage in Time and Charges Telephone Billing Systems among hotels and motels.
In this latter system an answer relay is operated by rectified 30 cycle ringing current which is super-imposed on the direct current loop. A make contact on the relay applies 117 volts of AC to operate a connect relay. The connect relay has a holding path through its own make contacts and disconnects the ring relay with a break contact arrangement. The 117 volt AC connect relay, upon operation, applies the start and operate current to the teletypewriter motor.
The motor is disconnected by a momentary interruption of the Connect Relay Coil Circuit by means of the normally closed contacts of "Slot 29". These contacts are operated by the EOT (end of transmission) coding and the Teletypewriter logic. This is a straight forward circuit requiring relatively large relays because of the contact current requirements.
The sensitivity of the present circuit is limited by available relays to meet the required parameters. The high make and break currents cause false characters known as "hits" on the line. These momentary errors are often evident at the beginning of a message. The standard relays require regular maintenance procedures.
A momentary loss of AC power, which sometimes occurs, causes the present relay circuit to drop out. Then the motor does not restart until another ring through. However, the message has been terminated.
Accordingly, an object of this invention is to provide a control arrangement that is more sensitive for use on longer transmission loops and that is insensitive to interruptions in commercial AC power at the remote locations.